Field of the Invention
The present invention relates to an image recording apparatus and a control method therefor.
Description of the Related Art
Recently, faster printers have longer printheads. Some full-line printers have a printhead with a width corresponding to a print page to speed up printing. Such printers can print a large area at once and hence can speed up printing as compared with conventional printers of a type designed to reciprocate a recording head. Along with the development of such printers, demands have arisen for higher processing speeds of conversion from print data into recording image data for actual recording by a printhead. Parallelization is one of techniques used for an increase in this processing speed. As a parallelization method, a method of dividing a printing area is known. This method can cope with an increase in printing width by increasing a division number, and hence can provide a system with high scalability with respect to the elongation of the printheads of printers (for example, Japanese Patent No. 4125717).
The above method, however, sometimes causes processing discontinuity between divided areas. When performing print control using adjacent pixels, it is sometime impossible to perform proper control because of a lack of information for the control. For example, such control includes non-discharge complementation control to be performed when a printhead cannot discharge any ink. Conventional non-discharge complementation is performed by assigning recoding image data to adjacent nozzles. When, however, performing processing upon dividing an area, recording image data cannot sometimes be assigned to adjacent nozzles, resulting in image quality deterioration such as white streaking. This problem causes serious image quality deterioration, in particular, in a full multi-printer designed to print on a printing area only once.
As a solution for such discontinuity, a method of sharing a memory is known. In this method, as the number of parallel operations increases, the amount of access to data in the memory per unit time multiplies. This may cause a decrease in processing speed. Consider, for example, a case in which each circuit for quantizing multi-valued image data requires a memory access data amount per unit time as 600 MBytes/sec. In this case, if the number of quantization circuits is increased to three to increase the number of parallel operations, it requires three times the access data amount, that is, 1,800 MBytes/sec. In practice, the accessible band of the memory has its own limit. Even if, therefore, the number of parallel operations is increased, a wait time for data acquisition from the memory occurs. That is, there is a limit to an increase in speed in accordance with an increase in the number of parallel operations.